1. Field of the Invention (Technical Field)
The present invention relates to decontamination methods and kits for decontaminating surfaces contaminated with actinides, other radionuclides, or heavy metals.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Although solutions of varying effectiveness exist for decontaminating surfaces contaminated with actinides, other radionuclides, and/or heavy metals, existing solutions often have limited effectiveness or pose additional environmental risks.
The main ingredients of past decontamination solutions have been complexing agents such as EDTA and citrate. Unfortunately, these reagents have a limited efficiency in the range of pH values of environmental interest. Most existing technologies are expensive, use harsh chemicals, are hazardous to workers, and create secondary mixed wastes that are not environmentally acceptable.
The use of isosaccharinate (“ISA”) or isosaccharinic acid (“HISA”) as a decontamination reagent overcomes many of these difficulties. Throughout the specification and claims, unless otherwise clear from context, “ISA” is used to refer to either of isosaccharinate or isosaccharinic acid. The past available data on ISA with tetravalent actinides have been very limited (limited to pH 12), empirical, and only related to determining actinide behavior in cementitious environments. ISA has heretofore been seen only as a danger to containment of radionuclides because it is a degradation byproduct of cellulose. Extensive work has been, done on characterizing and managing this danger. See, e.g., G. Fanger, et al., “Project SAFE: Complexing Agents in SFR”, Swedish Nuclear Fuel and Waste Management Company Report R-01-04 (2001); K. Vercammen, et al., “Complexation of Th(IV) and Eu(III) by α-isosaccharinic acid under alkaline conditions”, Radiochim. Acta 89:393-401 (2001); K. Vercammen, et al., “Evidence for the Existence of Complexes between Th(IV) and α-isosaccharinic Acid under Alkaline Conditions”, Radiochim. Acta 84:221-224 (1999); K. Vercammen, “Complexation of Calcium by α-Isosaccharinic Acid under Alkaline Conditions”, Acta Chemica Scandinavica 53:241-246 (1999); D. Rai, et al., “The Influence of isosaccharinic Acid on the Solubility of Np(IV) Hydrous Oxide”, Radiochim. Acta 83:9-13 (1998); D. Rai, et al., “Solubility of Crystalline Calcium Isosaccharinate”, J. Solution Chemistry 27:1109-1122 (1998); S. Holgersson, et al., “Effects of Gluco-isosaccharinate on Cs, Ni, Pm and Th Sorption onto, and Diffusion into Cement”, Radiochim. Acta 82:393-398 (1998); E. Wieland, et al., “Interaction of Eu(III) and Th(IV) with sulphate-resisting Portland cement”, Mat. Res. Soc. Symp. Proc. 506:573-578 (1997); L. van Loon, et al., “Sorption of isosaccharinic Acid, a Cellulose Degradation Product, on Cement”, Environmental Science & Technology 31:4:1243-1245 (1997); X. Bourbon, et al., “Influence of Organic Degradation Products on the Solubilisation of Radionuclides in Intermediate and Low Level Radioactive Wastes”, Radiochim. Acta 74:315-319 (1996); G. Baston, et al., “Sorption of Plutonium and Americium on Repository, Backfill and Geological Materials Relevant to the JNFL Low-Level Radioactive Waste Repository at Rokkasho-Mura”, Mat. Res. Soc. Symp. Proc. 353:957-964 (1995); B. Greenfield, et al., “The Identification and Degradation of Isosaccharinic Acid, a Cellulose Degradation Product”, Mat. Res. Soc. Symp. Proc. 353:1151-1158 (1995); A. Moreton, “Thermodynamic Modelling of the Effect of Hydroxycarboxylic Acids on the Solubility of Plutonium at High pH”, Mat. Res. Soc. Symp. Proc. 294:753-758 (1993); and E. Wieland, et al., “Immobilisation of Strontium, Nickel, and Iodide by a Sulphate-Resisting Portland Cement. 13 Radiochemical Conference, Czech Republic, p. 388 (1998).
The present invention is of decontamination methods and kits employing ISA, as well as of an improved method of making ISA. Although ISA forms strong complexes with all different oxidation states of actinides, the complexes it forms especially with tetravalent actinides are of the highest interest. This is because actinides (especially Pu and Th) are expected to be present in the tetravalent state, the state at which they are extremely insoluble and need to be removed for decontamination purposes. The present invention relates, therefore, in large part to decontamination via the tetravalent actinide complexes of ISA. Therefore, the present application presents: 1) fundamental data on ISA complexes with tetravalent actinides, in particular Th(IV) and Np(IV), in the entire range of pH values of environmental interest, so that comparisons can be made of its efficiency with the existing cleaning agents (e.g., EDTA and citrate); and 2) refined ISA preparation and purification techniques, so that large quantities of ISA can be produced cheaply and quickly, presenting a major advantage over other complexing agents which may work equally well in a limited range of pH values (e.g., siderophores) but which cannot be synthesized inexpensively.
ISA is environmentally friendly, easily biodegraded, and strongly chelates many metal ions in different oxidation states; therefore, it can be used in applications other than decontamination of radioactive contaminated surfaces. The ISA can be used alone, in addition to, or as an additive in cleaning products and solvents. This includes but is not limited to the use of ISA in solutions, foams, creams, powders, or other formulations and forms for cleaning and surface preparation (e.g., removal of metal ions). Additionally, ISA can be used alone or with other chelators such as citrate, EDTA, other organic/inorganic chelators and solvents, surfactants, cleaning agents, and wetting agents in cleansing formulations such as detergents, soaps, and metal stain removers. These other specific applications for which ISA-containing products can be used include: 1) radioactive decontamination of soils as in soil washing, soil flushing, leaching agent for soils in place or in a process where the soils are decontaminated in an above ground process; 2) decontamination of plants, animals, people, live stock, and buildings, because ISA is environmentally friendly and easily biodegradable; and 3) metal stain removal (e.g., iron, calcium, and rust) and decontamination agent for fabrics, steel, wood, concrete, leather, stone, marble, and glass, and other manmade materials.